Rename/rewrite recently added option and function in window.el

* lisp/window.el (window-at-x-y): Rename from `window-at-pos'.
Fix doc-string.
(delete-window-choose-selected): Rename from
`delete-window-set-selected'.  Fix doc-string.
(delete-window): Adjust to above renaming.
* doc/emacs/windows.texi (Change Window): Mention new option
`delete-window-choose-selected'.
* etc/NEWS:
* doc/lispref/windows.texi (Deleting Windows): Follow up on
above renamings.
8 jobs for master in 1 minute and 9 seconds (queued for 3 seconds)
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Name Stage Failure
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prep-image-base Prep Images There has been a runner system failure, please try again
Initialized empty Git repository in /builds/emacs/emacs/.git/
Created fresh repository.
From https://emba.gnu.org/emacs/emacs
* [new ref] 00140ca6bfceda53eb4f504b859e283d04c2c67f -> refs/pipelines/11050
* [new branch] master -> origin/master
Checking out 00140ca6 as master...

Skipping Git submodules setup
ERROR: Job failed (system failure): Error response from daemon: Conflict. The container name "/runner-2oEDrUT7-project-1-concurrent-3-build-4" is already in use by container "2fd6009bffdf866a8953b2d29eb4525d54954a49b699e714fb49c7f5568216a8". You have to remove (or rename) that container to be able to reuse that name. (executor_docker.go:726:0s)